Method and apparatus for printing sound film



Aug. 1, 1939. L. DEWAN 2,167,

METHOD AND APPARATUS FOR PBINTQLNG SOUND FILM Filed Dec. 11, 1937FlG..9. F|G.10.

IN V EN TOR. Le on D ewan A TTORNE Y.

I modification of the invention.

Patented Aug. 1, 1939 umrso STATES PATENT OFFICE aimuz .METHOD ANDAPPARATUS FOR PRINTING SOUNDFIIM Leon Dewan, New York, N. Y., asaignorof fifty per cent to George H. Callaghan, New York,

Application December 11.11937, Serial No. 179,294

3 Claims.

'printing of sound on film and has for its object the reduction andelimination of dirt spots, scratches and grain from a negative soundtrack during theprocess of photographic transference to a positive film.I

In this invention the object is. attained solely by optical means. Thenegative is untreated but its image on the positive film is somanipulated that with development of the positive film the undesireddirt spots do not appear or are greatly reduced in intensity while atthe same time the sound images are intact. A plurality of laterallydisplaced images of the negative are projected upon the positive film'in a manner that irregularities in the lateral plane of the sound trackare canceled optically in their eife'ct upon the finally developedpositive emulsion withoutaffecting the sound track whose values lie inthe longitudinal plane.

Figures 1, 2 and 3 are diagrams illustrating the principle of theinvention.

Figures 4 and 5 are diagrammatic top and side views of an apparatus forcarrying out the invention.

Figure 6.1llustrates a variation of Figures 4 and 5.

Figures 7 and 8 are diagrammatic views of a modification of theinvention.

Figure 9 is]; diagram illustrating the eilects produced by themodification illustrated in Figv ures 7 and 8.

Figure 10 is a diagram illustrating another Due to the nature ofphotographic emulsion, and the dust or dirt which acc ulates on film,

both variable width and variabl density negative sound track oftencontain small spots or irregularities on their clear portions after'development. Especially in the case of variable width track where theboundary between the black and transparent portions has a peculiarroughness due to irradiation and the finite width of the recording lightbar which affects high frequency and faint sounds to a considerableextent. This effect is greatly reduced in afeature about. to bedescribed. In Figure 1, illustrating roughly an ordinary variable widthtrack, the black spots on the clear portion'symbolizethe dirt spots orroughness. Figure 2 shows a positive of this negative track produced,for example, by optically projecting an image of the negative track 7upon a positive film. The spots that were formerly on a-clear field-arenow clear areas upon a black field. .11, instead of projecting a singleimage of the negative sound track upon the positive film, two or moreimages of, the same negative track are projected, these images exactlycoinciding longitudinally (in the direction of the length of the soundtrack) but slightly displaced laterally relative to each other, thenthose areas- The solid line represents one image and the dotted lineanother image of the same sound wave, and the shaded portions representthose parts of 1 the spots which are restored to blackness or opacity.

Naturally if one image of the negative track f creates full blackness onthe positive film by means of its luminous portions anothersimilar.image cannot greatly further blacken those portions of the positive filmwhich have already been acted upon, but can, if slightly displaced,blacken the parts that have been left unillumined by the first image.The greater the number of images that are used and the nearer they arespaced laterally; the more effective is this coverage. The imagesmayalso be spaced at unequal distances apart, to cover the range ofdifierent sizes of the spots or irregularities. The images may also beof difi'erent intensities so that while one or a number of images arecapable of producing full photographic intensity, another weaker imagewould only aitect the white spots when added to the light of otherimages, whilethe parts of the track on which it alone would fall wouldbe unaffected thereby due to the fact that its intensity is below thatpoint at which the positive emulsion starts to record any lightimpression.

If desired, a strong image of the negative sound track may be projectedon the positive film to produce full or almost full opacity thereon,while one or more slightly weaker images are projected therewith, eachone being displaced from the other a little nearer to the base line ofthe variable width sound track to cover the whitev spots andirregularities.

The printing apparatus shown in Figures 4 and 5. may produce two imagesof the negative sound track on the positive film. The negative film 'theplate such as 6 of Figure 4 may be as shown i is illumined by the lamp 2andthe spherical lens 3 focuses the image of the negative on thepositive film 4. The printing aperture 5 in the mask 5a is half coveredby a plane parallel glass plate 6 having a sharply defined edge. Thusthere is imaged on the film l the upper half of the printing aperture 5in one position and the lower half thereof in another position slightlydisplaced to one side due to the well known property of a parallel facedglass plate to displace an image to one side if the plate is presentedat an angle. Since thmfilms travel longitudinally (as indicated by thearrows) the result produced on the positive film when developed is twosuperimposed images laterally displaced with respect to each other inaccordance with the invention.

It may be seen that additional displaced images may be produced by thismeans; for example the printing aperture may be divided in three parts,the upper and-lower parts beingcovered by glass plates such as 6presented in different angles while the center portion is imageddirectly.

Where symmetric bilateral .variable width track is to be printedaccording to the invention in Figure 6 where the parts'ia and 6b ofplane parallel glass' are bevelled and cemented together, the centraljoining line being in alignment with the center of the bilateral soundtrack.

Figures 7 and 8 illustrate a method of producing the results of theinvention in a modified manner. The apparatus is mainly similar to thatof Figures 4 and 5 except thatin place of a plane parallel glass platethere is a convex cylindrical lens I which produces a laterally enlargedimage of the .sound track so that the result on the positive film l is anormal track imaged from the unobstructed part of the printing aperture5' and superimposed thereon, a track enlarged in the lateral plane onlyby the cylinder lens I.

Figure 9 shows the result on the positive with a bilateral variablewidth track. The areas of full density are those portions where bothimages overlap while the grey shaded areas are those covered by thenormal image only. It is evident that all parts of the enlarged imageare displaced from corresponding parts of the normal sized image inproportion to their distance from v the center of the track. Thus forexample if there is a small dirt spot in the negative film its laterallyenlarged image would be nearer to the edge of the sound track on thepositive film than its normal sized image and thus create the coveringeflect already described. Another effect may be observed in Figure 9coinciding with that already mentioned. This is the fact that thevalleys of the normal sized track are lightened by the lower intensityas indicated by the grey shaded portion,'which represents that coveredby the one image afione. The effect of this lower intensity is to clearor hollow out the valley where it tends to fill in as for example wherehigh frequency soundwaves are. recorded.

This result, of clearing or elongating the valleys without afiecting thepeaks, is desirable and has long been sought for-in the printing ofvariable width track.

The apparatus described so far is usable, for either variable width orvariable density track but the modification 'of the inventionillustrated in Figure 10 is designed to produce the general result ofthe invention in a manner specially suitable for variable density soundtrack. The spherical lens 3" images the negative sound track of film l"on the positive as in Figures 1 and 2 but the cylindrical convex lens 8defocuses 5 Thus while the sound waves which are resolved 10 inthe'longitudinal plane retain all their sharpness of definition, theimages of dirt spots and scratches are covered by light from other partsof the image in the lateral plane and the result is a considerableclearing up, particularlyeflec- 5 tive in the periods of low volumewhere clear spots on the dark background of the positive would otherwiseappear. Where reduction from 35 mm. to 16 mm. is accomplished by themodification of Figure 10 the mask 9 may have a much 20 wider apertureproportionately since the lens 8 produces the effect of thedisproportionate magnification required in transference of 35 mm. to 16mm. sound track. 1

What-is claimed is:

l. The method of photographically printing a longitudinally definedsound wave'track from plain film which normally contains vground noiseirregularities distinct from the sound waves, consisting in imaging saidsound wave track upon a sensitive film, producing a, plurality ofsuperimposed images of said sound wave track which accurately coincidein the longitudinal plane to define scanning of the sound waves, andlaterally displacing portions of one image relative to correspondingportions of another image to an extent substantially of the order of thesize of the ground noise irregularities, whereby portions of one imageshall fall upon different portions of g .irregularities' distinct fromthe sound waves,

consisting in imaging said sound wave track upon a sensitive film,producing a plurality of superimposed images of said sound wave trackwhich coincide accurately in the longitudinal plane to define scanningof the sound waves,

and laterally displacing portions of one image relative to correspondingportions of another image by causing the images to have unequal lateraldimensions, whereby portions of one image shall fall upon differentportions of the other image in the lateral plane.

3. The method of photographically printing a longitudinally definedsound wave track from 'film which normally contains ground noiseirregularities distinct from the sound waves,

consisting in imaging said sound wave. track '60 upon a sensitive film,producing a plurality of -superimposed images of said sound wave trackwhich coincide accurately in the longitudinal plane to define scanningof the sound waves,

and laterally displacing portions of one image relative to correspondingportions of another image so that said displaced portions are shiftedaway from either side of the center line of the 'track and toward theedges thereof, whereby portions of one image shall fall on differentportions of the other image in the lateral plane.

' LEON DEWAN.

